"Mutating viruses and resistance to drugs are the major challenges to overcome in influenza (flu) prevention and treatment. Virus-neutralizing antibodies are the key for protection against flu infection, but flu-specific CD4+ and CD8+ T cells play a significant role by providing help to B cells and in viral clearance, respectively.There are many vaccines against flu infection approved for human use. The generally effective seasonal vaccines, however, have a number of deficiencies, including the need to repeat the injections every year with a newly updated vaccine, which provides only antibody-dominated subtype-specific protection. Adjuvants are used to enhance the immune response to a vaccine. They lead to different types of cell-mediated immune responses. The T cell type (Th1, Th2, cytotoxic) and the magnitude of the immune response discriminate between viral clearance and immunopathology. Particular T cell subpopulations (like Th1 IFN-γ or CD8+ perforin or Fas expressing cells) may be responsible for protection after infection or vaccination and may give correlation to protective adjuvants.Studies of T cells using assays analyzing entire cell populations are not suitable to uncover these cell populations. We propose a detailed T cell differentiation profiling of CD4+ and CD8+ T lymphocytes at the single cell level after flu vaccination using the quantitative single cell multiplex RT-PCR method. Individual T lymphocytes purified from the vaccination site draining lymph nodes will be analyzed for the presence of up to twenty important differentiation markers. The results will be verified by additional methods, like flow cytometry or confocal microscopy.This project will reveal the presence of T cell subpopulations possibly correlated to protection after flu infection with mouse-adapted PR8 influenza strain or immunization with seasonal flu vaccine, with special consideration on the effect of adjuvants."